Reporting channel state information in a multiple component carrier network

ABSTRACT

A user equipment (UE) may determine channel state information (CSI) reports with each CSI report being related to a component carrier. The UE may send a subframe with CSI report(s) on a physical uplink control channel (PUCCH). When a collision occurs in the subframe having the CSI report(s) on the PUCCH a lower priority CSI report may be dropped from the transmission.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/483,699, filed Apr. 10, 2017, which is a continuation of U.S. patentapplication Ser. No. 15/137,940 filed Apr. 25, 2016, which issued asU.S. Pat. No. 9,622,227 on Apr. 11, 2017, which is a continuation ofU.S. patent application Ser. No. 13/948,852 filed Jul. 23, 2013, whichissued as U.S. Pat. No. 9,325,479 on Apr. 26, 2016, which is acontinuation of U.S. patent application Ser. No. 12/752,572 filed Apr.1, 2010, which issued as U.S. Pat. No. 8,520,491 on Aug. 27, 2013, whichare incorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention relates generally to communications and particularto communications over multiple carriers. More particularly, in certainembodiments the present invention provides a mechanism for periodicchannel state information signaling that employ carrier aggregation.

BACKGROUND

There has not been any significant prior work on related signalingdetails of periodic channel state information (CSI) with multipleparallel configurations in the case of multiple component carriers(CCs). Contributions in the Third Generation Partnership Project (3GPP)tend to focus on extending the physical uplink control channel (PUCCH)payload beyond 11 bits, which would permit new, larger CSI formats.

Activation and deactivation of component carriers has been discussed.There has also been some discussion about the concept of primary andsecondary component carriers in radio access network 2 (RAN2): primarycomponent carrier (PCC), and secondary component carrier (SCC),respectively.

SUMMARY

In one embodiment, the present invention is a method. The methodincludes determining, in an apparatus, channel state information. Thechannel state information includes channel state information of aplurality of component carriers. The method also includes reporting, bythe apparatus, the channel state information comprising a plurality ofreports in an aggregated form.

In a further embodiment, the present invention is an apparatus. Theapparatus includes at least one memory including computer program code.The apparatus also includes at least one processor. The at least onememory and the computer program code are configured to, with the atleast one processor, cause the apparatus at least to determine channelstate information. The channel state information includes channel stateinformation of a plurality of component carriers. The at least onememory and the computer program code are also configured to, with the atleast one processor, cause the apparatus at least to report the channelstate information comprising a plurality of reports in an aggregatedform.

In a further embodiment, the present invention is a computer-readablenon-transitory medium encoded with information that, when executed inhardware, performs a process. The process includes determining channelstate information. The channel state information includes channel stateinformation of a plurality of component carriers. The process alsoincludes reporting the channel state information comprising a pluralityof reports in an aggregated form.

BRIEF DESCRIPTION OF THE DRAWINGS

For proper understanding of the invention, reference should be made tothe accompanying drawings, wherein:

FIG. 1 illustrates an example of an implementation for handlingcollisions between channel state information reports.

FIG. 2 illustrates a method according to certain embodiments of thepresent invention.

FIG. 3 illustrates an apparatus according to certain embodiments of thepresent invention.

FIG. 4 illustrates a technique for constructing rules for handlingcomponent carrier aggregation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Channel State Information (CSI) feedback signaling with carrieraggregation may be useful in the Long Term Evolution (Advanced)(LTE-Advanced) of the Third Generation Partnership Project (3GPP)system, which may be a part of 3GPP LTE Release 10 (3GPP LTE Rel-10).

LTE-Advanced may serve as an evolution of the LTE Release 8 (Rel-8)system, fulfilling the International Telecommunication Union (ITU)Radiocommunication Sector (ITU-R) requirements for International MobileTelecommunications-Advanced (IMT-Advanced). Carrier aggregation will beone technology component aimed at providing high bandwidth and peak datarates for the new system.

An efficient way to provide channel state information (CSI) reportingfor multiple component carriers (CCs) can help to make efficient use ofaggregated spectrum. Periodic CSI signaling aspects on the physicaluplink control channel (PUCCH) and especially the rules and proceduresrelated to handling multiple CSI reporting configurations will bediscussed below.

Periodic reporting of CSI such as channel quality indicator (CQI),precoding matrix indicator (PMI), and rank indicator (RI) is thefundamental mode of feedback signaling in LTE Rel-8. The periodic CSIreports are carried on PUCCH, and the payload size is typically limitedto a maximum of 11 bits. Due to the limited payload size, the reportstypically contain little or no information about the frequency domainbehavior of the channel.

With carrier aggregation, the need for periodic CSI may remain.LTE-Advanced (Rel-10) may, for example, support approximately fivedownlink (DL) CCs. Hence the straightforward expansion of Rel-8reporting for multiple CCs would result in large reports (e.g. 5*11bits=55 bits). This may not be helpful from the uplink (UL) signalingpoint of view. First, such high overhead may limit uplink capacityconsiderably. Second, in many cases it may not be possible to guaranteesufficient UL coverage for such large payloads. Hence some compressionmethods may be used to reduce the UL signaling burden.

The most straightforward way to reduce the signaling load is toconfigure CSI reporting separately for each CC. This option can assiststandardization, maximizing the commonality with Rel-8 specifications.Furthermore, the DL transmission mode can be configured separately foreach DL CC, which would make joint encoding of the CSI reportscomplicated, or at least lead to a large number of supported options.

There are a number of ways that component carriers can be handled in acommunication system. For example, there can be explicit activation anddeactivation of configured downlink (DL) component carriers is done bymedia access control (MAC) signaling. There can also be implicitdeactivation of configured DL component carriers. The configuration of aDL/UL component carrier can be within a user equipment's (UE's)aggregation capability. As a consequence, activation/deactivation aswell can be within UE capability.

A newly configured component carrier can always be in a default state of“deactivated.” In order to activate a newly configured componentcarrier, an activation command may be necessary. Furthermore, DLcomponent carriers can be activated and deactivated individually. Asingle activation/deactivation command can activate/deactivate a subsetof the configured DL component carriers.

The uplink (UL) primary component carrier (PCC) and DL PCC can beconfigured per UE. The UL PCC can be used for transmission of L1 uplinkcontrol information. In certain embodiments, the DL PCC cannot bede-activated. Re-establishment can be triggered when the DL PCCexperiences radio link failure (RLF), as opposed to when other DL CCsexperience RLF. These implementations, however, are merely examples ofhow component carriers can be handled.

The following discussion focuses on the rules and procedures related tohandling multiple CSI reporting configurations. Such rules for handlingmultiple CSI reporting configurations may be useful when transmitting aCSI for multiple CCs simultaneously in the same subframe. This situationmay be described as being the state that exists when multipleconfigurations collide.

The rules and procedures may relate to handling periodic CSI reportingfor carrier aggregation using PUCCH with multiple parallelconfigurations. The multiple parallel configurations may be CC-specific.

For each configured DL CC, a periodic CSI reporting mode can beconfigured. Reporting disabled is here considered as a reporting mode, aspecial case of configuration. In other words, the reporting disabledcase can be considered a periodic report having the frequency of“never.” The configuration can be done using RRC signaling and includesparameters such as periodicity, subframe offset, reporting mode, PUCCHresource used for reporting etc.

For the primary component carrier (PCC) the UE can start reporting CQIafter it has received the CQI configuration via radio resource control(RRC) signaling. This follows similar procedures as in LTE Rel-8.

For the secondary component carriers (SCC) the UE can start to reportCQI according to the RRC configuration after it has received anactivation command for the given CC with media access control (MAC)signaling.

In the case of CC deactivation, the UE can stop reporting CSI for thatCC. In other words, there may be no requirement that the UE reportregarding inactive CCs.

In certain embodiments, when the periodic reports for two or more CCswould collide, the following complementary rules take place. The rulesare numbered for the sake of identification. Unless otherwise noted, oneshould not treat the numbers as though they were setting forth a fixedsequence, such that, for example, 2 must come after 1 and before 3.

Option 1 is multiplexing. In this option, when the PUCCH resources forthe colliding CSI reports are located on the same or the adjacent PRB,all the CSI reports can be sent simultaneously. Each UE may beconfigured to omit this option and always perform the dropping ofcolliding CSI reports according to the following options, which involveprioritization.

Option 2 gives infrequent reports a priority. In this option, the CCconfiguration with lowest periodicity is prioritized and the othersimultaneous reports are omitted. In the case of equal periodicity, aCSI corresponding to a predetermined CC is sent while the CSI(s)corresponding to other CC(s) is/are dropped, similar to Option 4discussed below.

Option 3 gives rank indicators priority. In this option, a reportcontaining RI is prioritized over CQI/PMI. In the case when the need totransmit them simultaneously occurs, CQI/PMI is dropped.

Option 4 ranks different CCs separately. The priority order fordifferent CCs can be configured separately. This can be done with e.g.RRC configuration. The configuration indicates in which order the CSIfrom different CCs is prioritized. In the case of collision the CSI forthe CC with higher priority is sent while the other one is dropped.

Option 5 gives priority to primary component carriers over secondarycomponent carriers. In this option, CSI reports for PCC are prioritizedover SCC.

Various combinations of different options are also possible. Forexample, Option 2 and Option 3 can be combined. Option 1 can be alsocombined with Option 2, 3, 4 or 5 in the case that some but not all CSIreports are located on the same or the adjacent PRB. Thus, for example,a first single CSI report according to one of options 2-5 is selected,and after that other CSI reports on same or adjacent PRB are alsoselected for transmission.

The reporting configuration for the DL PCC can follows the Rel-8principles. For the SCC(s) the CSI reporting can be masked with theactivation/deactivation command received via MAC signaling. There canbe, for example, a bitmap indicating which of the SCCs are activated ordeactivated.

An example of an implementation for handling collisions between CSIreports can be summarized with the block diagram shown in FIG. 1. Theembodiment of FIG. 1 shows a decision tree, which can be one way inwhich certain embodiments of the present invention is implemented.

As shown in FIG. 1, when the need arises to transmit CSI reports for twoor more CCs simultaneously occurs (first yes branch from the top of thediagram), a device can first check whether the PUCCH resourcesconfigured for transmission of the CSI reports are on a single, oralternatively on adjacent, PRBs. One reason for imposing such arestriction is that transmission on multiple non-adjacent PUCCHs couldviolate single-carrier properties, resulting in increased cubic metricand out-of-band emissions.

If the colliding reports meet the criteria, as illustrated, for example,in the second yes branch from the top of the diagram, the reports aresent according to their respective configurations. If the collidingreports do not meet the criteria, as illustrated for example, in thelower no branch, only the reports with highest priority are sent. Todetermine the highest priority, options 2, 3, 4, or 5, discussed aboveor a combination thereof can be employed.

Alternatively, the multiplexing functionality may also be configurable.For example, one can limit a cell edge user equipment (UE) not to sendmore than one CSI report at a time in any case.

The condition for concurrent transmission of multiple PUCCH Format2/2a/2b resources can be formulated in the following way (NxPUCCH Format2/2a/2b):

First, a physical resource block (PRB) index m can be defined for ak^(th) PUCCH Format 2/2a/2b resource asm(k)=└n _(PUCCH) ⁽²⁾(k)/N _(sc) ^(RB)┘where n_(PUCCH) ⁽²⁾ is the higher-layer configured resource index for aperiodic CSI transmitted on PUCCH and N_(sc) ^(RB) is the number ofsub-carriers (SC) per PRB (there may be 12 sub-carriers per resourceblock), respectively.

The criteria for concurrent transmission of multiple PUCCH format2/2a/2b resources can be formulated asm(k)∈[b,(b+2n)],where b is an integer and n∈[0, 1, . . . , N] where N is a predefinedinteger. Integer b can be defined as b=min(m(k)). This criteria ensuresthat PUCCH resources transmitted at the same time are located on thesame side of the system bandwidth. There are two special cases with n=Oand n=1:

n=0: PUCCH resources are located on the same PRB; and

n=1: PUCCH resources are located on adjacent PRBs.

In principle, PUCCH resources can be located on multiple adjacent PRBs.To also cover this case, the criteria can be checked sequentially: sortm(k) in increasing order, N=1, b=min(m(k)); and starting from smallestm(k), check criteria. If it is filled, update N=m(k)+1 for current k andcontinue.

Certain embodiments of the present invention may have variousadvantages. For example, certain embodiments of the present inventionmay permit independent configuration per CC, which may permit reuse ofthe Rel-8 functionality as much as possible. Additionally, since thereare no existing solutions for handling collisions between CSI reports,the approach above may be implemented widely, such as by means of astandard. Moreover, allowing for multiplexing of CSIs when they aretransmitted on a single or adjacent PRBs brings advantages in terms ofperformance, assuming that sufficient coverage can be guaranteed.

FIG. 2 illustrates a method according to certain embodiments of thepresent invention. The method can be performed by an apparatus such as aterminal, a user equipment, or a mobile node. The method of FIG. 2includes determining 210, in an apparatus, channel state information.The channel state information includes channel state information of aplurality of component carriers. The method also includes periodicallyreporting 220, by the apparatus, the channel state informationcomprising a plurality of reports in an aggregated form. An aggregatedform can include several independent reports. The periodically reporting220 can be performed via a physical uplink control channel.

The method can include preparing 215 the aggregated form. The preparing215 can include dropping 217 at least the channel state informationreport for at least one configuration based on a priority. It should benoted that a configuration for a component carrier may include more thanone report.

After channel state information of a first component carrier is selectedfor inclusion in the aggregated form based on a priority, other channelstate information corresponding to component carriers that have the sameor an adjacent physical resource block can also be selected forinclusion in the aggregated form. The priority can be, for example,lowest periodicity of reporting. In other words, the highest prioritycan be assigned to a component carrier whose report is to be sent themost infrequently.

As may be understood from the discussion above, a computer-readablenon-transitory medium can be encoded with information that, whenexecuted in hardware, performs a process corresponding to the processdisclosed in FIG. 2, or any other process discussed herein. Bynon-transitory medium, it is meant that the medium is not a transitorysignal. Examples of non-transitory mediums include a computer-readablemedium, a computer distribution medium, a computer-readable storagemedium, and a computer program product.

Channel state information for component carrier configurations havingequal periodicity can be prioritized according to a predeterminedranking for component carriers. Channel state information for componentcarrier configurations comprising a rank indicator can be prioritizedabove channel state information for component carrier configurationscomprising channel quality indicator or precoding matrix indicator.Alternatively, or in addition, a plurality of component carrierconfigurations can be individually assigned a predetermined priority.Channel state information for primary component carriers can beprioritized over channel state information for secondary componentcarriers.

FIG. 3 illustrates an apparatus according to certain embodiments of thepresent invention. The apparatus can include at least one memory 310including computer program code 320. The apparatus can also include atleast one processor 330. The apparatus can be configured to communicateusing a transceiver 340, including a receiver portion 343 and atransmitter portion 347, with a base station or enhanced node B (notillustrated). The apparatus can use an antenna 350 to communicate withthe base station or other network element over a wireless link 360,which may be a cellular radio link. The apparatus can be configured toprepare reports regarding, for example, downlink (DL) quality forcomponent carriers of the wireless link 360.

In the process, the at least one memory 310 and the computer programcode 320 can be configured to, with the at least one processor 330,cause the apparatus at least to determine channel state information. Thechannel state information can be channel state information of aplurality of component carriers. The at least one memory 310 and thecomputer program code 320 can also be configured to, with the at leastone processor 330, cause the apparatus at least to periodically reportthe channel state information comprising a plurality of reports in anaggregated form.

The at least one memory 310 may be any suitable form of memory, such asthe onboard memory of a controller chip, a hard drive, various types ofRandom Access Memory (RAM), or Read-Only Memory (ROM). The computerprogram code 320 can be any appropriate form of computer instructions.The computer program code 320 may be provided in a compiled orinterpreted form. The processor 330 can be any suitable processingdevice, such as but not limited to a Central Processing Unit (CPU),controller, or Application Specific Integrated Circuit (ASIC).

FIG. 4 illustrates a technique for constructing rules for handlingcomponent carrier aggregation. As illustrated in FIG. 4, the techniquecan begin by selecting 410 a prioritization technique from a variety oftechniques. Four such techniques are illustrated, although othertechniques are permitted.

The first of the four techniques shown is to prioritize 420 byfrequency/periodicity of reports. That is to say, a CC report that is tobe infrequently reported may be given a higher priority than frequentlyreported CC reports or vice versa.

The second of the four techniques shown is to prioritize 430 bypreferring RI over CGI/PMI (or vice versa). This technique permits themost important aspects of a CC report to be given priority over thosethat the system considers less important.

To prioritize 440 by ranking CCs in separate, predetermined ways is thethird of the four techniques shown in FIG. 4. In this technique, eachindividual CC may be assigned a predetermined ranking and may beprioritized according to the predetermined ranking.

The fourth technique of the four techniques in FIG. 4 is to prioritize450 by preferring CSI reports for PCCs over those for SCCs. Thistechnique can permit the reports for PCCs to be given a preference, whenit is not feasible to report on both PCCs and SCCs. Like the otherpriority schemes it can be reversed, if desired, such that SCCs aregiven a priority over PCCs.

Finally, in addition to the selected CC report of the various availableCC reports, the system can multiplex 460 any “close” reports. In thiscase, “close” can refer to reports for the same or an adjacent physicalresource block (PRB).

One having ordinary skill in the art will readily understand that theinvention as discussed above may be practiced with steps in a differentorder, and/or with hardware elements in configurations which aredifferent than those which are disclosed. Therefore, although theinvention has been described based upon these preferred embodiments, itwould be apparent to those of skill in the art that certainmodifications, variations, and alternative constructions would beapparent, while remaining within the spirit and scope of the invention.For example, although certain embodiments of the present invention havebeen discussed in relation to 3GPP system, it should be understood thatthe present invention may be applied to other system such as the EvolvedUniversal Terrestrial Radio Network (E-UTRAN) and the like. In order todetermine the metes and bounds of the invention, therefore, referenceshould be made to the appended claims.

What is claimed is:
 1. A method of operating a user equipment (UE), themethod comprising: determining whether at least two of a plurality ofchannel state information (CSI) reports are to be transmitted on aphysical uplink channel, each of the plurality of CSI reports related toa respective one of a plurality of component carriers; on a conditionthat the determination is positive, dropping at least one lower priorityCSI report of the plurality of CSI reports, wherein: a CSI reportcontaining a Rank Indicator (RI) is prioritized over one or more CSIreports containing a Channel Quality Indicator (CQI), and a CSI reportcontaining a RI for a higher priority component carrier is prioritizedover one or more CSI reports containing a RI for a lower prioritycomponent carrier; and transmitting, subsequent to the dropping, atleast one prioritized CSI report of the plurality of CSI reports on thephysical uplink channel.
 2. The method of claim 1, wherein the physicaluplink channel is a physical uplink control channel (PUCCH).
 3. Themethod of claim 1, wherein the determining whether at least two of aplurality of CSI reports are to be transmitted on a physical uplinkchannel occurs on a subframe basis.
 4. The method of claim 1, whereineach of the plurality of component carriers has an associated priority,the method further comprising: on a condition that there are no CSIreports for a primary component carrier, dropping at least one lowerpriority CSI report of the plurality of CSI reports, wherein a CSIreport containing a RI for a component carrier with a highest associatedpriority is prioritized over one or more CSI reports containing a RI fora respective component carrier of lower associated priority.
 5. A userequipment (UE) comprising: a processor operable to determine whether atleast two of a plurality of channel state information (CSI) reports areto be transmitted on a physical uplink channel, each of the plurality ofCSI reports related to a respective one of a plurality of componentcarriers; the processor further operable to, on a condition that thedetermination is positive, drop at least one lower priority CSI reportof the plurality of CSI reports, wherein a CSI report containing a RankIndicator (RI) is prioritized over one or more CSI reports containing aChannel Quality Indicator (CQI), and a CSI report containing a RI for ahigher priority component carrier is prioritized over one or more CSIreports containing a RI for a lower priority component carrier; and atransmitter operable to transmit, subsequent to the dropping, at leastone prioritized CSI report of the plurality of CSI reports on thephysical uplink channel.
 6. The UE of claim 5, wherein the physicaluplink channel is a physical uplink control channel (PUCCH).
 7. The UEof claim 5, wherein the processor is operable to determine whether atleast two of a plurality of CSI reports are to be transmitted on aphysical uplink channel occurs on a subframe basis.
 8. The UE of claim5, wherein each of the plurality of component carriers has an associatedpriority, and the processor is further operable to, on a condition thatthere are no CSI reports for a primary component carrier, drop at leastone lower priority CSI report of the plurality of CSI reports, wherein aCSI report containing a RI for a component carrier with a highestassociated priority is prioritized over one or more CSI reportscontaining a RI for a respective component carrier of lower associatedpriority.
 9. A non-transitory computer readable storage mediumcomprising executable code stored thereon that, when executed by aprocessor, causes a user equipment (UE) to: determine whether at leasttwo of a plurality of channel state information (CSI) reports are to betransmitted on a physical uplink channel, each of the plurality of CSIreports related to a respective one of a plurality of componentcarriers; on a condition that the determination is positive, drop atleast one lower priority CSI report of the plurality of CSI reports,wherein: a CSI report containing a Rank Indicator (RI) is prioritizedover one or more CSI reports containing a Channel Quality Indicator(CQI), and a CSI report containing a RI for a higher priority componentcarrier is prioritized over one or more CSI reports containing a RI fora lower priority component carrier; and transmit, subsequent to thedropping, at least one prioritized CSI report of the plurality of CSIreports on the physical uplink channel.
 10. The non-transitory computerreadable storage medium of claim 9, wherein the physical uplink channelis a physical uplink control channel (PUCCH).
 11. The non-transitorycomputer readable storage medium of claim 9, wherein the determinationof whether at least two of a plurality of CSI reports are to betransmitted on a physical uplink channel occurs on a subframe basis. 12.The non-transitory computer readable storage medium of claim 9, whereineach of the plurality of component carriers has an associated priority,further causing the UE to: on a condition that there are no CSI reportsfor a primary component carrier, drop at least one lower priority CSIreport of the plurality of CSI reports, wherein a CSI report containinga RI for a component carrier with a highest associated priority isprioritized over one or more CSI reports containing a RI for arespective component carrier of lower associated priority.